Telefacsimile transmission system



A. G. COOLEY TELEFACSIMILE TRANSMISSION SYSTEM Filed March 25, 1958Sv-Shqets-Sheet 2 l INVENTOR ATTORN Y Oct. 8, 1940.`

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TELEFACSIMILE TRANSMISSION SYSTEM Filed March 25, 1958A- .Oct. 8, 1940.

INVEB'AS? BY fd/f ATTORNEY Patented Oct. 8, 1940 PATENT OFFICETELEFACSIMILE TRANSMISSION SYSTEM Austin G. Cooley, New York, N. Y.,assignor to Wide World Photos, Inc., New York, N. Y., a corporation ofNew York Application March 25, 1938, Serial No. 197,991

9 Claims. y (Cl. 1785.6)

This invention relates to telefacsimile transmission and more especiallyto systems for transmitting facsimiles between widely separatedlocalities, employing existing telephone, telegraph "10 phone wirechannel; and also transmitting from the same source to one or moredistant receiving points over a carrier telephone channel.

Another object is to provide a system of telefacsimile transmission froman originating source 5 over existing telephone service lines, to aplurality of distant receiving points some of which are linked to thetransmitting source via noncarrier lines, and others of which are linkedto the said source via carrier lines.

Another object is to provideA an improved repeater arrangement fortelefacsimile transmission over existing telephone service lines,whereby the transmission can be effected from an originating point by anon-carrier wireline to a main re- ,25 peating point and from whichlatter point transmission may be repeated over either'non-carrier wirelines or carrier wire lines to distant receiving points, withoutduplicating separate or complicated synchronizing equipment at eachpoint. A feature of the invention relates to a repeating arrangement fortelefacsimile transmission over existing telephone service lines,whereby compensation for frequency drift or other form of distortionintroduced by a carrier link, can be v indicated and eiected at acentral point. This enables the facsimile signals to be faithfullyreproduced at a plurality of distant receiving points, notwithstandingthat the signals during transmission have passed over a non-carrier wirechannel and over a carrier wire channel.

Another feature relates to an improved form of drift indicator tocompensate for frequency' 55 plished by delaying the repeating of thesignals fromthe more expensive toll connected stations until the othertollconnections have been fully completed, and the called subscriber hasanswered the telephone.

A still further feature relates to the novel or- ,-5 ganization,arrangement and interconnection of parts constituting an economical andexible repeating arrangement for telefacsimile transmission.

Other features and advantages not specifically 1,10 enumerated will beapparent after a consideration of the following detailed descriptionsand the appended claims. n

Since the invention is concerned primarily with a telepicturetransmission and a repeating system J5 as a whole, only those parts ofthe system as are necessary to a full understanding of the invention aredescribed and illustrated in detail. The details of apparatus which arewell known'vin the art are omitted for the sake of clarity and in order20 to enable the invention to be more readily understood. It isunderstood therefore, that wherever in the specication and drawings adevice or apparatus is illustrated schematically in block diagram form,that any suitable apparatus well 25 known to the art may be employed.vAccordingly, in the drawings, p

Fig. 1 is a schematic block diagram showing the invention applied to atypical existing telephone service network. 30

Fig. 2 is a more detailed diagram of part of the system of Fig. 1.

Fig. 3 is a schematic block diagram of a modification of the invention.Y

Fig. 4 is a detailed diagram of the drift cor 35 rector and indicatorarrangement that may be used in the system of Fig. 3. f

Where telefacsimile signals are to be transmitted from an originatingsource to a plurality of receiving points, over existing telephoneservv4.0 ice lines, it frequently happens that one or more receivingpoints are linked to the originating` points by a carrier channel, andother receiving points are linked to the transmitting point by anon-carrier channel. As pointed out in Patent I15 No. 2,138,398, thecharacteristics of the usual carrier terminal equipment are such thatupon demodulation of the modulated carrier, a frequency drift distortionmay be introduced. Consequently, where the synchronizing signal istransmitted over the same channel as the facsimile signal proper, thereceiving equipment Amay run out of step with the transmitter. This isespecially so where the picture signal is transmitted in the form of amodulated pulsating or alternating current of fixed fundamentalfrequency which frequency is used for synchronizing, as described forexample in Patent No. 2,045,294, granted to Austin G. Cooley. Inaccordance with the present invention, the frequency drift correction iseffected at a central or intermediate point in the system, and a specialform of indicator is used tovindicate when correction is required.v

Furthermore, when facsimile transmission is effected by employing theusual telephone sube scribers calling and answering equipment, and thetransmission is to be effected tov va plurality of receiving points, oneor more of the called points may be slow to answer the telephone calland if the transmission has been started, the slow-to-answer subscriberwill receive only part of the transmission. Or if transmission has notbeen started, it may require that other expensivetoll connections mustbe held up until the slowt'o-answer subscriberremoves his receiver tocomplete -the connection. As an example, assume that a picture is to betransmitted from Boston to New York and thence repeated to Philadelphiaand Toronto. It is quite obvious that when the Boston subscriber makeshis call to the New York subscriber, and the latter is informed thatYthe picture is'to be repeated to Philadelphia and Toronto, the New Yorksubscriber thereupon calls the Philadelphia and Toronto subscribers.Consequently, even though the New York subscriber is in readiness toreceive and repeat the picture signals, he must await the answer of thetelephone bythe Philadelphia and Toronto subscribers respectively.Should both the Philadelphia and Toronto subscribers answer their callssimultaneously, then of course the transmission can be effected fromBoston to NewYork and thence repeated to Philadelphia and Toronto.Should however, the Toronto subscriber be slow in answering histelephone or should the toll connection to Toronto be delayed, it isnecessary to hold up the previously completed telephone connectionsuntil the Toronto subscriber answers his telephone. In the case of longtoll connections, the holding timevof the previously completed trunkconnections during this preliminary setting up of the connections' mayconstitute avery expensive procedure. In accordance with the presentinvention, this disadvantage is overcome by receiving the picture andrecording it in the usual way at the New York station 'and Vrepeating itsimultaneously to thefnearby'station, but delaying the transmission tothose stations where the completion of the toll connection is likely tobe delayed. l

Referring to Fig. -1, there is shown diagrammatically a typical set upof telephone lines for effecting facsimile transmission, it beingassumed that the picture is to be transmitted from Boston to the variouspoints designated. Each of the dotted rectangles of Fig. vl represents atelephone 'subscribers station in the particular locality designated. Itis assumed that the telephone connection from Boston to New York is overa lnon-carrier wire line, while the connection from New York to SanFrancisco is over a carrier telephone line. In the drawings, the wire ornon-carrier telephone channels connecting the various localities areindicated by the full lines whereas the carrier telephone channels areindicated by the dot-dash lines. The pictureto be transmitted is'analyzedand translated into a series of current impulses byanywell-known apparatus designated` by the numeral I." For a detailedldescription of such apparatus, reference may be had to Patent No.1,593,651, granted to Austin G. Cooley. Preferably, the apparatus I isof such a character that the picture signals are transmitted in the formof an alternating or pulsating -current having a definite fundamentaltelephone frequency which is modulated in accordance with the shadecharacteristics of the successive analyzed elemental areas of thepicture. For example, the fundamental frequency may be 1800 cycles persecond, and this 1800 cycle component can be used as the synchronizingcontrol signal. The picture modulated current is then applied to thetelephone line 2 in any Well-known manner. Preferably, although notnecessarily, the application is effected in the manner described indetail in application Serial No. 103,506, led October l, 1936, so thatin effecting connection between Boston and New York, all that the Bostonsubscriber has to do is to remove his telephone receiver from its switchhook and ask the telephone operator to connect lhis line with theparticular line in New York over which the transmission is to beeffected.

`.The New York subscriber is provided with a photographic recorder 3 andalso with a phonographic recorder 4. Associated with the recorder v4 isa phonographic repeater 5 by means of which the retransmission over theline 6 to the Toronto subscriber may be delayed. The Toronto subscriberis of course provided with a photographic recorder I which may besimilar to the recorder 3.

The New York subscriber is also provided with a repeater 8 preferably,although not necessarily, of the type disclosed in application SerialNo. 149,868, filed June 23, 1937. This repeater has a plurality ofoutput coupling members by means of which the repeated currents may beapplied to the respective telephone lines leading to the Philadelphia,Miami, Nashville, etc. subscribers each of these latter subscribersbeing provided with a photographic recorder I3, I4, I5, etc. similar torecorders 3 and 'I. At the New York subscribers station, there is alsoprovided a phonographic repeater 9 by means of which the phonographicrecord produced on recorder 4 may be translated back into thecorresponding picture currents. The output of repeater 9 is coupled,preferably, although not necessarily, as described in said applicationSerial No. 149,848, to the carrier telephone line leading to the SanFrancisco subscribers station.4 The repeater 9 is preferably driven by asynchronous motor I0 which is operated from a suitable tuning forkoscillator II. The fork oscillator is of such frequency that it causesthe motor I0 to operate the drum or table of-repeater 9 so that the waxdisc or the wax cylinder on the repeater 9 on which the picture currentshave been recorded, makes one complete revolution for each 2400 forkimpulses, it being understood that the picture drum of the transmitter Iat the Boston station is also driven so that it makes one completerevolution for each 2400 impulses of the picture current. In otherwords, the current in the output of repeater 9 consists cf a fundamentalfrequency of 1800 cycles per second modulated in accordance with theshade characteristics of the original picture at Boston. At the SanFrancisco subscribers station, there is provided a photographic recorderI2, which may be similar to the recorders 3, lI, I3, I4 and I5. Therecorder I2 is preferably driven in synchronism with the repeater 9 bymeans of a tuning fork controlled oscillator I6 similar to theoscillator II. A portion of the 1800 cycle picture currents received atthe San Francisco ter that transmission is to be recorded at New l Yorkand repeated to Philadelphia, Miami, Nashville and Toronto. The New Yorksubscriber while maintaining the original connection with Boston thencalls 'the subscribers at the designated points and when the telephoneconnections have been completed, a suitable signal is transmitted to theBoston subscriber, whereupon the apparatus I is set in operation andtransmits the ypicture currents to the New York subscriberY where theyare photographically recorded on the recorder 3 and phonographicallyrecorded on the recorder 4. A portion of these picture currents are alsorepeated immediately by repeater 8 over the several telephone lines toPhiladelphia, Miami and Nashville. Assuming that it takes a longer timeto effect the telephone connection to the Toronto subscriber than itdoes to the Philadelphia subscriber, the phonographic repeater 5 isoperated in time displaced relation with respect to the phonographicrecorder 4 andthis time displacement may be Variable so as to allow theToronto sub-scriber to come in on the connection without losing any ofthe transmission. When the transmission over the wire telephone lineshas been completed, the phonographic record is removed from the recorder4 and mounted on another phonographic repeater 9 which may be similar tothe repeater 5, with this diiference however, that repeater 5 ismechanically connected to run at the same speed as recorder 4, whereas,repeater 9 is operated at a speed determined by the tuning forkcontrolled oscillator II-. The New York subscriber having placed andcompleted the toll connection to the San Francisco subscriber sets therepeater 9 in operation and the picture currents are transmitted overthe carrier telephone line to the San Francisco central oice where theyare demodulated by the usual central ofce carrier telephone demodulatingequipment and the San Francisco subscriber therefore receives a currenthaving an approximate 1800 cycle fundamental frequency and withmodulations corresponding to the shade characteristics of the originalpicture transmitted from Boston. The photographic reproducer I2 isdriven in synchronism with the repeater 9 under control of the localtuning fork oscillator I6 so that the drum of recorder I2 makes onecomplete revolution for each 2400 impulses of the received picturecurrent. The fork oscillator I6 which controls the recorder i2 also actsas a source of carrier current for retransmission of the picture signalsto the Los Angeles subscriber. For this purpose, a portion of thecurrents received by the San Francisco subscriber are detected by thedetector I'l and modulate the current from the fork oscillator and themodulated output from modulator i8 is applied to the wire telephone lineleading to the Los Angeles subscribers station. At the latter station,there is providedv a photographic recorder I9 similar to the recorder 3.Consequently, the recorder I9 'can be operated in synchronism`with thertransmitter I and the synchronism can be effected over the wirechannels by the fundamental frequency of the picture currentsthemselves, While over the carrier channel portion of the connection thesynchronism is effected by the fork controlled oscillators. Referring toFig. 2, there is shown in somewhat more detail the important parts ofthe equipment at the Boston, New York Aand San Francisco subscribersstations referred to in the set up of Fig. 1. At the Boston station, thepicture to be transmitted is wrapped around the scanning drum 25 whichis driven through suitable gearing 26 from a non-synchronous motor 2l,motor 27 also drives the toothed wheel 28 of an induction generator,which rotates adjacent a coil 29 and by means of which a current of 1800cycles per second is generated in the circuit including coil 29,transformer Winding 30 and battery 3 I.

The secondary winding 32 is connected in circuit with the photoelectriccell 33, resistance 34 and battery 3`5. Light from a suitable steadysource 36 is projected through condensing lens 31 on to the picture, andthe reected light is passed through the objective lens 38, thencethrough the apertured mask 39, to the cell 33. The electric variationsset up by the cell 33, and the 1800 cycle current in secondary 32 areimpressed across the input electrodes of `a suitable grid-controlledvacuum tube or audion 40, with the result that there is produced in theoutput of said tube 40 a current of a fundamental frequency of 1800cycles modulated in accordance with the shade values of successiveelemental areas of the picture. It will be understood of course, thatthe drum 25 is advanced longitudinally, a predetermined amount for eachrevolution thereof. Preferably, although not necessarily, eachrevolution of drum 25 corresponds to 2400 impulses of current fromgenerator 29. For a more detailed description of this portion of thesystem, reference may be had to Patent No. 1,593,651, granted to AustinG. Cooley. The modulated 1800 cycle impulses may be amplified further bya suitable vacuum tube amplifier 4I and then impressed upon thetelephone line 42 by a coupling unit 43, it being understood that theBoston subscriber has meanwhile called the New York subscriber who hasanswered the call in the usual way of placing a telephone call. Unit 43may be of any Well-known construction but is preferably of the typedisclosed in said application Serial No. 103,506.

' At the New York subscribers station, there is provided a pick-up unit44 which may be similar to unit 43. The output of unit 44 is amplifiedby a suitable vacuum tube amplifier 45, and is applied to the primarywinding 46 of a transformer which is provided with three separatesecondary windings 4l, 48, 49. Winding 4`I is connected to the inputelectrodes of a suitable vacuum tube .amplifier 50, the output of whichis applied through coupling transformer 5I, to the recording lamp 52, asuitable apertured mask 53 be-` ing located between the lamp and thesensitized paper wrapped around the scanning drum 54. A suitable opticalsystem represented schematically by lens 54a forms on the sensitizedfilm an image of the illuminated aperture in mask 53. Drum 54 is drivenpreferably by a 90 cycle synchronous motor 55 which in turn iscontrolled by a 90 cycle generator 55, the latter being driven by an1800 cycle synchronous motor 5'I which in turn is #controlled by the1800 cycle current from winding 48 after amplification by tube 58. The

to motor through transformer 60. Motor 55 rotates drum 54 in synchronismwith drum 25 `thus causing the transmitted picture to be reproduced onthe sensitized lm wrapped around drum 54 in the well-known manner.

For the purpose of retransmitting the 1800 cycle picture currents toanother subscriber, for example the Toronto subscriber (Fig 1), thecurrent in secondary winding 49 after amplification in tube 6|, isapplied to a coupling transformer having a primary winding 62 and twoseparate secondary windings 63, 64. The current in winding 63 afteramplification in vacuum tube 65, is fed through coupling transformer 66to the recording head 61 of a suitable electromagnetic recording devicehaving a stylus which is oscillated in synchronism with the currentsfrom transformer 66, as is well known in the phonographc and soundrecording arts. Associated with the recording stylus 61 is a cylindricaldrum. 68 on which is mounted a cylindrical wax blank, the drum with theblank being rotated at the desired speed by a motor 69 preferably,

`although not necessarily, of the synchronous type.

Also associated with drum 68 is a phonographic translator 1| which ispreferably mounted to be moved longitudinally of the drum, so as toStart the phonographic reproduction at any desired part of the record asis well known in the phonograph and dictaphone arts. Device 1Itranslates the phonographic record into corresponding electric currents.1t will be understood of course, that the heads 61 and 1I may be mountedin threaded engagement with a suitable lead screw so as to move theheads longitudinally in timed relation to the rotation of drum 68, itbeing understood that by suitable decoupling means, for example a splitnut coupling with the lead screw,

,each head may be adjusted to any desired position longitudinally of thedrum end. The phonographic currents generated by reproducer 1l are thenapplied to a coupling device 12 which may be similar to devices 43 and44 and by means of which the 1800 cycle picture modulated currents areapplied to the telephone line 13 leading to the Toronto subscriber. Itwill be understood that the New York subscriber has previously placed acall and has been connected in the usual way with the Torontosubscriber. From the foregoing, it will be seen that the phonographicrecord is being made by device 61 at the same time that the picture isphotographically recorded on drum 59. Consequently, should any timeelapse between the completion of the telephone connection to the Torontosubscriber and the beginning ofthe photographic recording, this may betaken care of by advancing reproducing head 1I so that the repeating ofthe phonographic currents to the Toronto subscriber does not take placeuntil the latter has answered the telephone call and is in readiness toreceive the currents. Consequently, no portion of the picture is lost bythe Toronto subscriber.

, When the transmissionis tobe repeated over a carrier telephonechannel, there may be introduced what is known as a frequency drift.There are disclosed in said Patent 2,138,398, certain methods ofcompensating for this frequency drift in order to use the fundamentalfrequency of the picture currents for syn- 4a suitable modulatingarrangement.

No. 1,691,071. 4fore a modulator as well as an amplifier, the

chronizing. However, where Asuch 1 frequency' drift compensation is notdesired, the synchronizing may be effected locally atthe New Yorksubscribers station and at the receiving subscribers station. Forexample, assume that the pictures are to be yrepeated from New York toSan Francisco. After the received picture currents have been recorded onthe wax blank on drum (i8l as above describedthis blank may betransferred to another similar drum 14 which is driven-by an 1800 cyclesynchronous motor 15, the drum being advanced longitudinally in theproperv timed relationY similar to the advancement and rotation of thedrum 25 at the transmitter. The motor 15 is controlled by a tuning fork16 Which. is associated with a vacuum tube amplifier 11. The'ampliedcurrents resulting from the interaction of the tuning fork and theamplifier tube are applied to motor 15. Preferably the motor 15 isgeared to the drum 14 so that the latter makes one revolution for each2400 impulses from the fork 16 in order that the reproduction by thereproducing head 18 may be at the same rate as the scanning at theBoston transmitter. The currents from reproducer 18 vare applied to thecarrier telephone line 19 pref- .windings 82, 83. Winding 82 impressesthe picture currents on the recording lamp 84 the light from whichpasses throughl a suitable apertured mask-85 and a lens system 85 toyform an elemental light spot on the sensitized film wrapped around therecording drum 81. Drum 81 is driven by a synchronous motor 88 which iscontrclled by a tuning fork 89 and amplifier arrangement 90 is similarto the tuning fork 16 at the New York station. Consequently, the picfture currents are received and reproduced at the same rate as they wereoriginally transmitted from the Boston oflice. Should it be desired toretransmit the picture from San Francisco to Los Angeles over thenon-carrier telephone line 9i, and without employing a localsynchronizing source at the Los Angelesl subscribers station, thesynchronism may be effected by the frequency of the picture currentsthemselves. For

this purpose, a portion of the` picture currents rreceived at the SanFrancisco station are applied through transformer winding 83 to asuitable vacuum tube detector 92 in the output circuit of which thereare produced currents corresponding yto the shade values of the originalpicture. Associated with the tuning fork 89 is a pick-up coil 93 bymeans of which la current of 1800 cycles per second is impressed uponthe coupling transformer 94. The currents in the secondary of thetransformer 94 and the detected picture current from tube 92 areimpressed upon Since ,the output of detector` 92 is in effect a variableamplitude D. C. signal the tube 95 and associated input circuitincluding resistance 96 and battery 91 are 4of the so-called directcoupled amplifier type as illustrated for example in U. S. Patent Thetube 95 is in reality theremodulating signal ,beingderived from forkf89.

zamlrwy There is thus produced in the output of tube 95 an 1800 cyclecurrent modulated in accordance with the original picture-signals', andthis current may be coupled to the telephone line 9| bya coupling device98 similar to devices 43, 44, 'IZFand 80. At the Los Angeles station,there is provided a photographic recorder 99 similar to recorders 54 and8l, which is operated in synchronism with the transmitter drum by the1800 cycle component of the received picture currents.

Fig. 3 shows a modification of the invention wherein all stations, fromthe originating station kto the various receiving stations, aresynchronized by a frequency component of the picture currents.

`InKFig. 3, the picture is assumed to be transmitted from the SanFrancisco subscriber by means of picture transmitting apparatus such asdescribed forY example in connection with the Boston transmitter (Fig.2) the transmission being over a non-carrier channel to the Sacramentosubscriber who is equipped with recording and .repeating mechanism suchas disclosed in said application Serial No. 149,848. The pictures arerecorded at the Sacramento station and are repeated by carrier telephoneto the Omaha sub- Scriber Where they are repeated over the noncar-nier`line |0I to the Chicago subscriber. Assuming the'transmitter atthe SanFrancisco station produces a picture signal in the form of an 2,1800`cycle modulated wave, then therecording apparatus at Sacramento will besynchronized by the 1800 cycle component. However, .because of thecarrier telephone link between Sacramentoand Omaha, the carrierdemodulating equipment in the telephone plant may intro- .duce afrequency drift or distortion by the time the picture signals arereceived by the Chicago subscriber.V In order to maintain proper synchronismby the synchronizing component of the picture, notwithstandingthis frequency drift, a frequency drift compensator can be employedv atthe Chicago station. One form of such compensator is disclosed in saidPatent 2,138,398. Breferably, the drift compensator is locatedv at anintermediate point of the system, for example" at Chicago, the picturesignals beingpreferably received from the telephone line |0|, by an4inductive coupling device |02 as disclosed in said application SerialNo. 103,506. being-acted on by the compensator |00, the picturecurrentsare applied to the photographic reproducer |03 which is synchronized bythe-1800 cycle component of the currents flowing from the ,cernpensator|00. These compensatedcurrents arealso repeated through respectiverepeaters |04, |05, |06, to the associated telephone lines leading'torother subscribers as shown. Each of these other subscribers is provided,with a photographic recording mechanism which is maintained-insynchronism by the 1800 cycle com` .ponent of the received picturecurrents.

` Preferably, the drift compensator |00 is of the type shown in Fig. 4l,wherein the conductors |01, |08, correspond to the same conductors ofFig. 3. For purposes kof explanation, let it be assumed thatthelSOQcycle picture current repeated from Sacramento is changed by thecarrier telephone Vequipment in the telephone plant at Omaha, so thatthere is repeated to Chicago a picture current of 179,9` cycles persecond. In order to effect proper synchronism at Chicago and succeedingstations, it is necessary therefore, to convert this19.9...yclecl0dulated picture current into a After similar 180.0 Vcyclecurrent.. v5 `The.1'799 cycle Acurrent receivedover conductors |01 isapplied to a modulator tube |09 of the audion type which is alsofed'with current from a source of oscillations 0 of known fixed, buthigher, frequency. For example, source ||0 may Agenerate asustained waveof 10,000cy'cles vper second.v The upper beat frequency between the 1799cycles and tht-:10,000 vcycles is, then applied toa demodulator tubevIl'of the audion type which yisalso fedfrom'a source l |2of sustainedWavesbut of variable frequcnifso .that in the output circuit ofthedemodulator ||'|,th`ere` is produced an 180|), cycle wavefjbearingftheoriginahpictiire` modulations. Thus 'under the above assumption,

the @sallam u2 is adjusted to beat witnthe `ing the compensator prior toactual reception of the picture signals, it is necessary that theoscillators l l0 .and ||2 be synchronized at the same frequen cy.V Forthis purpose, the oscillators may be connected to -the coordinatedeflectin'g plates..

HB, -I l1 of a cathode-ray tube oscilloscopeof any well-knownconstruction. `An attendant can by examining the patternV traced on thefluorescent screen of the oscilloscope, determine,r instantaneouslywhetherfthe sources H0 and I|2 are synchronoussynchroniaed and thepicture signals are received overconductors |01, the r`attendant candetermine by observing` thetarget H3 whether the oscillator I|2 shall beincreased or decreased ,in

After .the oscillations have been frequency so as tomaintainian. y18.00cyclecurrentfinH conductors |08. Q If the picture currents that arerepeatedthrough the Omahastation to Chicago v are also' to be recordedlocally at-the .Omaha Station. then @local frequency drift comscribersstation so ,that the local recording ythereat caribe compensated for'frequency driftin the manner described in said Patent 2,138,398.

While specific apparatusy and f circuit arrange- ,45 pensatorlmayfbe:provided `at the l.Omalfla subments have been Yreferredjto herein, itwill be understood that various changes -andmodifications may be madewithout departing `from the spirit and scope of the invention. f

1. In a telefacsimilerepeating system, a rst telephone subscribers'station,.a second telephone subscribers station, a third telephone subscribers station, a non-carrier telephone line linking vthefirstandsecond stations, a carrier .11

telephone line linking the second and third stations lwhich line lissubject to frequency drift in the telephone plant, means at said firststation including a facsimile scanner to generatev picture currents inthe .form'of an audiofrequency carrier whosefrequency is locked vwiththe/speed of the transmitting scanner, a picture reproducing means atsaid second station including motive means controlled by said carrier,means to repeat the picture currents from the second station tothe-third station over said carrierline, the. last mentioned meansincluding a tuning fork .controlled phonographic repeater at the secondstation, anda tuning fork controlled photographic. reQQrder theV Saidthird Station duceV the picture ,therefrom substantially free from theeffects of frequency drift in said carrier channel.

r2. Af system according to .claim 1 in which a @fourth vtelephonesubscribers station is connectedby a non-carrier line to said thirdstation, said third station having means to detect the picture signalmodulations in the picture currents received thereat and means tomodulate a regular frequency current controlled by the tuning fork atsaid third Vstation by said detected currents, said modulated .currentsbeing applied totheline leading to the fourth station, and a nel inseries with a carrier channel which is subject to Vfrequency drift,means located bef tween the junction of said physical and .carrierchannels to overcome the effects of said frequency drift, thelast-mentioned means including a beat frequency modulator onv which thereceived picture currents from the carrier channel are impressed and abeat frequency demodulator connected to the output of said modulator,and a facsimile reproducing mechanism at said distant station having itsvscanning mechanism synchronized with the transmitting scanner undercontrol of the output of said demodulator.

4. In a facsimile system of thetype wherein the facsimile signals aregenerated in the form of a modulated audio frequency current whosefrequency is locked with the speed of the transmitting scanner, whichsignals are to be transmitted to a distant station over a physicalchannel in series with a carrier channel which is subject to frequencydrift, means to repeat the signals from the carrier channel to thephysical channel so as to be free from the effects of frequency driftwhile maintaining synchronism with the transmitting scanner, thelast-mentioned means including a pair of oscillators, means to beat thepicture currents received from the carrier channel with one oscillatorto Yproduce a beat frequency, means to lbeat the said beat frequencywith another oscillator to produce another beat frequency, and means toapply said other beat frequency to said physical channel to control thefacsimile reproducing light source of a receiver'connected thereto andvto synchronize the facsimile scanning mechanism thereat with saidtransmitting scanner.

5. In a facsimile system of the type wherein the facsimile signals aregenerated in the form .of a modulated audio frequency carrier whosefrequency is locked with the speed of the transmitting scanner whichsignals are to be trans- 6. In a facsimile systemof the type whereinlthe-facsimile signalsV are generated in the form to' receive therepeated currents and to repro-` of a modulated audio frequency currentwhose frequency is locked with the speed of the transmitting scannerwhich signals are to be transmitted to a distant station over a physicalchannel in series with a carrier channel which is subject to frequencydrift, frequency drift compensating means between said channelsincluding a pair of normally synchronized oscillators, a beat frequencymodulator for producing a beat bef tweenthe first oscillator and thesignal currents, abeat frequency demodulator'having its output'controlled by the output of said modulator and the second oscillator,one of said oscillators being adjustable as to frequency in order tomaintain a predetermined fixed frequency in the signals applied to saidphysical channel, a facsimile reproducing mechanism at the receiving end,of said physical channel and having a scanner mechanism synchronizedwith the transmitting scanner by said fixed frequency,. and means as-fvthe facsimile signals are transmitted over a physicalchannel in serieswith a carrier channel which is subject to frequency drift, meansincluding a transmitting scanner to transmit facsimileA signals in theform of an audiofre-r quency current over said carrier channel to arepeater station while maintaining the facsimile transmitting andvreceiving scanners at the ends of saidcarrier channel synchronized bylocal os'-,A cillators, and means to retransmit said signals over saidphysical -channel to a distant station, the last-mentioned meansincluding a detector for detecting the signal modulations as receivedfrom said carrier channel, means to derive an audio frequency carrierfrom the oscillator local to said repeater and for modulating saidderived audio frequency carrier by said detected modulations, afacsimile reproducer at said distant station having means to synchronizeit with the .transmitting scanner under control of the said frequency ofsaid derived carrier whereby the facsimile reproduction at said distantstation is substantially free from the effects of frequency drift insaid carrier channel. f

8. In a system for transmitting facsimiles between a first station and asecond station which are linked by a physical telephone channel inseries with a carrier channel which is subject to frequency drift in thetelephone plant, means at said first station to transmit facsimilesignals in the form of a modulated audio frequency carrier, anintermediate station located between the physical and carrier channels,means at said intermediate station to record and to retransmit saidsignals under control of the record, the speed of said recording meansbeing locked with the transmitting mechanism at the first station 'bythe intermediary of said audio frequency carrier, a third stationconnected to said intermediate station by said carrier channel, means atsaid third station to retransmit said signals to said second station inthe form of a modulated audio frequency carrier substantially free fromthe effects of frequency drift in said carrier channel, thelast-mentioned means including a local source of oscillations at saidthird station, means v at said third station to detect the picturesignals received over said carrier channel, meansat saidy third stationto modulate said local oscillations by said detected signals, means totransmitsaid modulated oscillations to said second station. and afacsimile reproducer at said second -station which is synchronized withthe transmitter at the rst station by the frequency of said receivedoscillations.

9. The method of transmitting facsimiles over a carrier telephonechannel which is subject to frequency drift in the telephone plant,which method includes the steps of transmitting the facsimiles in theform of a modulated carrier Wave, receiving the modulated Wave anddetecting the signals therefrom, generating local oscillations at thereceiving station Whose frequency is independent of the frequency driftintroduced in said carrier channel, modulating said local oscillationsby said detected signals, retransmitting said modulated localoscillations to a third station in the form of an audio frequencylcarrier Whose frequency is locked with the transmitting scanner,recording the picture at said third station under` control of thereceived signals and controlling the synchronism of the recorder at saidthird station by said received carrier frequency.

AUSTIN G. COOLEY.

